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排序方式: 共有148条查询结果,搜索用时 468 毫秒
1.
Alcindo A. Dos Santos Renan S. Ferrarini Jefferson L. Princival João V. Comasseto 《Tetrahedron letters》2006,47(50):8933-8935
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin. 相似文献
2.
J.P. Contour A. Défossez D. Ravelosona A. Abert P. Ziemann 《Zeitschrift für Physik B Condensed Matter》1996,100(2):185-190
An energy model has been used to calculate the critical thickness h c of YBaCuO thin films and YBaCuO based superlattices within an isotropic or anisotropic approximation. The critical thickness of single layers calculated from the anisotropic model (16 nm) is in good agreement with the previously published experimental values which are spread out from 4 to 20 nm. In the case of superlattices, relaxation appears to be governed by the critical thickness of the elementary sub-layers and is then better evaluated through the calculation performed for YBaCuO single layers. XRD measurements on YBa2Cu3O7/PrBa2Cu3?xGaxO7 superlattices grown on {100{ SrTiO3 have evidenced a tetragonal stress in the YBaCuO ab plane which remains expanded when the YBaCuO elementary layer thickness is lower than 4.8 nm (4 YBaCuO cells). However the critical temperature of the shortest period superlattices is only slightly affected by this expanded stress in contrast to the effect of an elastic stress externally applied along the ab plane of YBaCuO thin films. 相似文献
3.
4.
P. J. Ziemann A. W. Castleman Jr. 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,20(1):97-99
Gas phase (MgO) n + and (MgO) n Mg+ clusters were produced in a gas aggregation source and studied by using laser-ionization time-of-flight mass spectrometry. A MgO molecule apparently serves as the nucleus for cluster growth, to which Mg and O atoms add. The heat generated by the formation of metal-oxygen bonds, and that added to the cluster by ionization leads to the production of clusters with the stoichiometry of the stable high-temperature oxide. The abundance maxima observed in the mass spectra indicate that the clusters form compact cubic structures similar to pieces of the MgO crystal lattice. The primary fragmentation channel responsible for the observed patterns is probably the loss of MgO monomers. 相似文献
5.
6.
Poliana Cristina Spricigo Banny Silva Barbosa Correia Karla Rodrigues Borba Isabela Barroso Taver Guilherme de Oliveira Machado Renan Ziemann Wilhelms Luiz Henrique Keng Queiroz Junior Angelo Pedro Jacomino Luiz Alberto Colnago 《Molecules (Basel, Switzerland)》2021,26(12)
The cambuci is a native Brazilian fruit from the Atlantic Forest biome. A soft and astringent pulp, a green color, and a sweet aroma are its main characteristics. Classical food quality attributes (fresh fruit mass, fruit height, diameters, total soluble solid, titratable acidity, and ratio) and the metabolic profile from ten accessions from three different locations were analyzed herein by analytical methods (refractometry and neutralization titration) and nuclear magnetic resonance spectroscopy. Concerning sugar content, sucrose was the predominant compound, with glucose and fructose alternating in second, depending on the accession. Citric acid was the most relevant acid, followed by shikimic and quinic acids in quite variable amounts. These three main acids vary in amounts for each accession. Ascorbic acid content emerges as an important quality attribute and makes this fruit nutritionally attractive, due to values comparable to those contained in citric fruits. The main amino acids identified in cambuci were glutamic acid individually or in comprising the tripeptide glutathione (glutamic acid, cysteine, glycine). The quality diversity of the evaluated accessions suggests the potentiality of cambuci use in future breeding programs. 相似文献
7.
Víctor Sánchez Marlon Rodrigues Garcia Michelle Barreto Requena Renan Arnon Romano Leonardo de Boni Francisco E. G. Guimarães Sebastião Pratavieira 《Photochemistry and photobiology》2020,96(6):1208-1214
Photodynamic procedures have been used in many applications, ranging from cancer treatment to microorganism inactivation. Photodynamic reactions start with the activation of a photosensitizing molecule with light, leading to the production of cytotoxic molecules that promote cell death. However, establishing the correct light and photosensitizer dosimetry for a broadband light source remains challenging. In this study, we proposed a theoretical mathematical model for the photodegradation of protoporphyrin IX (PpIX), when irradiated by multi-wavelength light sources. The theoretical model predicts the experimental photobleaching (temporal change in PpIX concentration) of PpIX for different light sources. We showed that photobleaching occurs independently of the light source wavelengths but instead depends only on the number of absorbed photons. The model presented here can be used as an important mathematical approach to better understand current photodynamic therapy protocols and help achieve optimization of the doses delivered. 相似文献
8.
B. Koslowski S. Strobel P. Ziemann 《Applied Physics A: Materials Science & Processing》2001,72(3):311-317
We have investigated the mechanism underlying the surface conductivity observed for synthetic diamond(001) samples. It is
found that (1) the surface conductivity depends on the pressure of the surrounding gas atmosphere, (2) the temperature dependence
can be described as being due to a thermally activated process and (3) a chromogeneous WO3 cathode turns color from transparent to blue and gas bubbles develop underneath the cathode if an electrical dc current is
passed through such an arrangement. In contrast, the complementary WO3 anode neither changed color nor were gas bubbles observed. One concludes that hydrogen develops at the negatively biased
WO3-diamond interface, recombining to gaseous H2. However, most of the hydrogen invades the WO3 cathode coloring it blue, thereby clearly indicating the involvement of protons. Though the conductivity crucially depends
on temperature, time and history of a sample, the resistances of various and even differently prepared diamond specimens covering
eleven orders of magnitude can be scaled onto one master curve reflecting a thermally activated behavior. Taken together,
we propose that the mechanism of the diamond(001) surface conductivity as observed under ambient conditions is at least partly
due to proton conduction.
Received: 13 April 2000 / Accepted: 31 July 2000 / Published online: 22 November 2000 相似文献
9.
M. Manolova V. Ivanova D.M. Kolb H.-G. Boyen P. Ziemann M. Büttner A. Romanyuk P. Oelhafen 《Surface science》2005,590(2-3):146-153
In this study we describe details of a new technique that allows to deposit metal on top of a self-assembled monolayer (SAM). Monoatomic high platinum islands were formed on a 4-mercaptopyridine SAM on Au(1 1 1) by first immersing the SAM-covered gold electrode in an aqueous solution of K2PtCl4 without potential control to allow Pt(II) ions to form a complex with the pyridine nitrogen. The complexed Pt(II) ions were then reduced electrochemically to Pt(0) after transferring the electrode to a Pt(II) ion-free solution. Upon reduction, monoatomic high Pt islands were observed in STM, the total coverage depending on the time for complexation. Ex situ angle-resolved XPS studies reveal that the Pt islands indeed reside on top of the SAM. 相似文献
10.
Cariou R Graham TW Dahcheh F Stephan DW 《Dalton transactions (Cambridge, England : 2003)》2011,40(20):5419-5422
Oxidative addition of an aryl-halide to Ni(COD)(2) in the presence of an equivalent of amino-bis-phosphinimine ligand affords complexes of the form [HN(CH(2)CH(2)N=PPh(3))(2)Ni-Ar][X] (Ar = C(6)H(4)F, C(6)H(5), X = Cl, Br) while the analogous reactions with 2 equivalents of Ni yield the amido-bridged complexes N(CH(2)CH(2)N=PPh(3))Ni(2)Br(3) and N(1,2-C(6)H(4)N=PPh(3))Ni(2)Br(3). 相似文献